1. Technical Field
The present invention relates to devices for processing optical data typical of which are optical pick-up devices for reading data from optical discs, and devices for writing data in photomagnetic discs or reading data therefrom. The optical pick-up device is adapted to converge laser light from a semiconductor laser or the like, project the converged light to the data record portion of the optical disc and read data according to the variations of intensity of the light reflected from the portion.
2. Prior Art
With the introduction of optical disc memories of high record density into use in recent years, it is expected to develop efficient, compact and lightweight optical pick-up devices.
Conventional optical pick-up devices consist primarily of an optical system and a drive system.
Basically, the optical system has the function of converging laser light on the record portion of an optical disc by a condenser lens and converting the light reflected from the disc into electric signals by a photodiode. Thus, variations in the amount of reflected light due to the data recorded on the disc are taken out in the form of electric signals.
Such optical systems are divided, according to their action, into isolator optical systems for separating the light reflected from the optical disc from the light impinging on the disc, beam converging optical systems for converging the light to be projected onto the optical disc to a spot of about 1 micron in diameter, and error detecting optical systems for detecting focusing errors or tracking errors. These optical systems comprise a suitable combination of elements such as a semiconductor laser serving as a light source, various lenses, prisms, diffraction grating, mirror, quarter wave plate and photodiode.
Useful drive systems include a focusing drive system, tracking drive system and a radial feed drive system.
The focusing drive system is adapted to maintain a suitable distance between the condenser lens and the optical disc so that the light beam formed by the condenser lens forms a proper spot on the disc surface. Most commonly, the condenser lens is moved axially thereof for adjustment.
The tracking drive system is adapted to cause the laser spot to follow the track of the optical disc without displacement. The mechanisms generally used for this purpose include one for moving the condenser lens perpendicular to the optical axis for adjustment, one for moving the entire optical pick-up head radially of the optical disc for adjustment, and one comprising a pivotable mirror for adjusting the angle of incidence of light on the condenser lens.
The radial feed drive system is a mechanism for feeding the optical pick-up head radially of the optical disc usually by a linear motor.
These conventional optical pick-up devices have the following drawbacks.
The optical system, which is complex, is cumbersome to optically align the components, which are liable to become out of alignment due to vibration.
The device comprises a large number of components, takes much time to assemble and is low in productivity.
The device comprises expensive optical components and is expensive in its entirety.
Use of large optical components renders the device large-sized, while the means needed for holding the optical components make the whole device heavy.